You can see a lot of what's going on with a e.g. DevTools in Chrome. Right click -> inspect You'll want to go to the performance tab, and then record and relo

You can see a lot of what's going on with a e.g. DevTools in Chrome. Right click -> inspect You'll want to go to the performance tab, and then record and reload the page (ctrl-shift-e). For me, about 3/4ths of the time is spent 'scripting' which is 'JS and DOM work'. It's not terribly enlightening, though, because all the JS is minified and takes some work to understand.